This invention relates generally to optical apparatus for viewing a wide angle input field and providing a wide angle output field image at unit magnification and also providing rotation at the output field about one or more axes. The invention relates particularly to optical apparatus for viewing a wide-angle scene and for providing pitch and roll motions for a wide-angle visual display for ground-based craft flight simulators.
Conventionally, in ground-based flight simulators a visual display projector is mounted on the craft cockpit which itself is mounted on the platform of a motion system. The projector projects an image forwardly onto a display screen which is viewed by a trainee pilot from inside the craft cockpit. The function of the pitch and roll optical apparatus of the invention is to receive light from the display projector and to direct its output light onto the display screen while providing pitch and roll rotations of its own output with respect to its input from the display projector.
Conventionally also, pitch and roll optical systems comprise rotatable pitch and roll prisms, which are separately rotatable to provide the pitch and roll motions of the viewed display. Such known pitch and roll systems are effective and adequate for small field angle displays.
For specific purposes, wide angle displays are required. For example, a helicopter flight simulator might require a visual display the field angles of which might be 180.degree. (.+-.90.degree.) in azimuth, together with 60.degree. (+15.degree., -45.degree.) in elevation/declination.
Such very large field angles present major problems in the design of a suitable pitch and roll optical system, firstly to provide the very large input and output field angles without introducing blurring, aberration or distortion, or even vignetting, of the image and secondly to provide a region within the system where the field angles and the beam diameter are both sufficiently small to permit inclusion of the rotatable pitch and roll prisms.
The general object of the invention is to provide improved optical apparatus of the type described above for viewing a wide-angle field and providing a wide-angle display.
The particular object of the invention is to provide such an optical system which is compatible with the above mentioned design requirements in providing a practical pitch and roll system for use with a wide-angle display projector wherein the output is a pencil beam, such as for example a scanned-laser projector.
Accordingly, the invention provides optical apparatus for receiving radiation from a wide-angle input field, and transmitting the radiation into a wide-angle output field, said transmission being such that the output field is an image of the input field formed substantially at unit magnification, and for providing rotation at the output field with respect to the input field, said optical apparatus comprising a concave axially-symmetric aspheric mirror and a convex axially-symmetric aspheric mirror having complementary reflecting surface shapes, approximately paraboloids, at the foci of which the entrance and exit pupils of the system are located, and an optical system in the radiation path between the two mirrors comprising reflecting prisms and two imaging systems of equal focal length and complementary distortion located such that their inner focal surfaces coincide at an intermediate pupil image and their outer focal surfaces are respectively near the two aspheric mirrors such that the surfaces of the two aspheric mirrors are imaged one onto the other at substantially unit magnification and without distortion, the optical axes of the two aspheric mirrors and of all elements of the two imaging systems being imaged onto a common line by reflection in the reflecting prisms, the reflecting prisms being rotatable to provide deflection of reflected radiation and of the optical axes of elements in the path of reflected radiation, so that radiation received from an input field at a first of the two aspheric mirrors is transmitted to the second of the two aspheric mirrors and reflected from it into an output field formed substantially at unit magnification and so that the output field is rotatable with respect to the input field.